Capacitor for semiconductor device and method of forming the same

ABSTRACT

A capacitor for a semiconductor device includes a lower electrode, a dielectric layer formed on a lower electrode, and an upper electrode formed on the dielectric layer. The lower electrode includes a first layer having a cylindrical shape and a mesh second layer formed on inner sidewalls and the bottom surface of the first layer. Beneficially, the first layer is connected to a conductive region of a semiconductor substrate by a contact plug. The lower electrode can be formed by injecting a catalyst into an opening in which the cylindrical first layer is to be formed before forming the cylindrical first layer.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 from Korean PatentApplication No. 2003-85919, filed on Nov. 29, 2003, the contents ofwhich are hereby incorporated herein by reference in their entirety forall purposes as if fully set forth herein.

BACKGROUND & SUMMARY

1. Technical Field

The present invention relates to a capacitor for a semiconductor deviceand a method of forming the same. More particularly, the presentinvention relates to an improved capacitor having a high capacitance anda method of forming the same.

2. Description of the Related Art

Recently, as information media such as computers have become widelyused, the semiconductor industry has made great strides in thedevelopment of the information media products. Functionally,semiconductor devices with a large storage capacity are required tooperate at a very high speed. Accordingly, semiconductor technology hasimproved the degree of integration, the reliability, and the responsecapability in order to increase the operating speed of semiconductordevices.

A dynamic random access memory (DRAM) has been the most widely usedsemiconductor memory device because of its ability to randomlyread/write data, and its high storage capacity. In general, a DRAMdevice includes a memory cell region to store data as an electriccharge, and a peripheral circuit region through which data istransferred as an electrical signal. The memory cell usually includes anaccess transistor and a storage capacitor.

The size of the capacitor has been reduced as the degree of integrationof the memory devices has increased. Research has been widely conductedfor a method of manufacturing a smaller, high-capacitance capacitor. Inparticular, a method of increasing the capacitance without increasingthe capacitor's surface size has been studied in recent years.

The capacitance can be increased by: (1) increasing the surface area ofthe storage electrode, i.e., the lower electrode of the capacitor; (2)reducing the thickness of the dielectric layer; and/or (3) increasingthe dielectric constant of the dielectric layer.

Conventionally, metal oxides such as Ta₂O₅, TiO₂, Al₂O₃, Y₂O₃, ZrO2,HfO₂, BaTiO₃ and SrTiO₃ have been used for the dielectric layer becauseof their high dielectric constants, as disclosed in U.S. Pat. No.5,316,982, issued to Taniguchi et al. However, reducing the thickness ofthe dielectric layer has its own limits in view of the high degree ofintegration of the memory device. In addition, although various highdielectric constant materials, and various methods for manufacturingdielectric layers using the same, are widely known, it is difficult toadapt the dielectric materials in manufacturing the dielectric layer.

Accordingly, increasing the surface area of the storage electrode hasbeen regarded as the most efficient method of improving the capacitanceof a capacitor.

To increase the surface area of a storage electrode, the capacitor hasdeveloped from an initial plane structure to a stack structure or atrench structure, and from the stack structure to a cylindricalstructure or a fin structure. For example, U.S. Pat. No. 5,656,536discloses a conventional stacked structure capacitor having a crownshape; and U.S. Pat. No. 5,716,884 and U.S. Pat. No. 5,656,536 discloseother conventional stacked structure capacitors having a fin shape. U.S.Pat. No. 5,807,782 discloses a conventional method of increasing thecapacitance by forming a hemispherical grain (HSG) layer on a storageelectrode of a capacitor; and U.S. Pat. No. 5,877,052 discloses yetanother conventional method of forming a HSG layer on a storageelectrode having a cylindrical shape using a method disclosed in U.S.Pat. No. 5,956,587.

However, the conventional methods of increasing the capacitance usingthe HSG layer has problems because a critical dimension (CD) betweenstorage electrodes cannot be reduced to a desirable degree, and the HSGlayer is often separated from the storage electrode to generate aprocess failure between two adjacent storage electrodes known as a“bridge”. Accordingly, the conventional methods described above havemany problems in forming capacitors with a design rule less than 0.14μm. Therefore, a cylindrical shaped capacitor with an increased heighthas been mainly used.

Examples of methods of forming the cylindrical capacitor are generallydisclosed in Korean Publication Patent Nos. 2001-83402, 2001-73561 and2001-4189 and U.S. Publication Patent No. 2001-4189.

FIGS. 1A and 1B are cross sectional views illustrating a conventionalmethod for forming a one-cylinder-stack (OCS) structured capacitor.

Referring to FIG. 1A, an insulating interlayer 12 is formed on asemiconductor substrate 10, and a contact hole 14 is formed by partiallyetching insulating interlayer 12, to expose a conductive region such asa source region (not shown) of semiconductor substrate 10. Then, aconductive material such as a doped polysilicon is filled into contacthole 14, to form a storage node contact plug 16.

An etching stop layer 18 of nitride, and a mold layer 20 of oxide aresequentially formed on insulating interlayer 12 and storage node contactplug 16. Subsequently, mold layer 20 and etching stop layer 18 areetched by an etching process, to form a storage node hole 22 to exposestorage node contact plug 16.

A storage electrode layer 26 such as a polysilicon layer is formed onthe bottom and sidewalls of storage node hole 22 and on the top surfaceof mold layer 20, and an oxide material is formed on storage electrodelayer 26 to a sufficient thickness to fill storage node hole 22, therebyforming a sacrificial layer 24.

Sacrificial layer 24 and storage electrode layer 26 are removed toexpose mold layer 20 by an etch back process or a chemical mechanicalpolishing (CMP) process, to form storage electrode 26 separated inaccordance with each node of a memory device.

Referring to FIG. 1B, any residual of sacrificial layer 24 remaining instorage node hole 22 and mold layer 20 is removed by a wet etchingprocess.

According to the conventional method described above, the height of thestorage electrode is high to increase the capacitance, thus mold layer20 is formed as thick as possible. In general, the thicker the moldlayer 20, the greater the slope of storage node hole 22. Accordingly,the critical dimension (CD) around a bottom portion of storage node hole22 is very small. A bottom portion of storage electrode 26, which isformed shallow and high, is narrow relative to a top portion of thestorage electrode. Thermal stress generated in subsequent processescauses weak storage electrodes to break, thus creating bridge failuresbetween two adjacent cells as depicted by reference numeral 28 in FIG.1B. That is, a process failure is generated over two unit cells (2-bitfailure).

In addition, the higher the storage electrode, the greater the stepdifference between a capacitor region and a non-capacitor region of asubstrate, creating difficulties in the subsequent processes.

Korean Publication Patent No. 2003-75907 discloses forming at least onemold layer and at least one support having different etching rates,prior to performing an etching process to form a storage node hole.Therefore, the support prevents the storage electrode from breaking.However, this Patent has disadvantages in that additional processes arerequired to form the support such as a deposition process and an etchingprocess. And also the processes to form the insulating interlayerdisposed between the conductive structure and the storage electrode arevery complicated.

Accordingly, it would be desirable to provide a capacitor for asemiconductor device capable of minimizing the step difference betweenconductive region and non-conductive region, and optimizing the surfacearea of the lower electrode.

According to an aspect of the present invention, a capacitor for asemiconductor device includes a semiconductor substrate, a lowerelectrode formed on the substrate, wherein the lower electrode comprisesa first layer and a mesh second layer, a dielectric layer formed on thelower electrode; and an upper electrode formed on the dielectric layer.

According to another aspect of the present invention, a method offorming a capacitor for a semiconductor device includes forming a moldlayer on a semiconductor substrate, forming a storage node hole toexpose a conductive region of the semiconductor substrate by etching themold layer, providing a catalyst into the storage node hole, forming alower electrode having a first layer and a mesh second layer, and thefirst layer connected to the conductive region of the semiconductorsubstrate, forming a dielectric layer on the lower electrode, andforming an upper electrode on the dielectric layer.

Beneficially, a surface area of the lower electrode is sufficientlyincreased by the mesh second layer so that the capacitance of thecapacitor is noticeably increased.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and advantages of the present invention willbecome readily apparent by reference to the following detaileddescription in view of the accompanying drawings, in which:

FIGS. 1A and 1B are cross sectional views illustrating a conventionalmethod of forming a one-cylinder-stack (OCS) storage electrodestructured capacitor;

FIG. 2 is a cross sectional view illustrating a capacitor of asemiconductor device according to one or more aspects of the presentinvention; and

FIGS. 3A to 3J are cross sectional views explaining a method of formingthe capacitor shown in FIG. 2.

DESCRIPTION OF THE EMBODIMENTS

In the description to follow, it will be understood that when an elementsuch as layer, region or substrate is referred to as being “on” or“onto” another element, the element is either directly on the otherelement, or intervening elements may also be present.

FIG. 2 is a cross sectional view illustrating a capacitor of asemiconductor device.

Referring to FIG. 2, an insulating layer 105 having a contact hole 110is formed on a semiconductor substrate 100. Contact hole 110 exposes acapacitor contact region such as a transistor source region, or alanding pad electrode (not shown) of substrate 100 which is electricallyin contact with a source region. A contact plug 115 electrically incontact with the capacitor contact region is disposed in contact hole110.

A lower electrode 140 of a capacitor C is disposed on insulating layer105. Lower electrode 140 includes a cylindrically shaped first layer 140a electrically in contact with contact plug 115, and a second layer 140b in the form of a 3-dimensional mesh, disposed within cylindrical firstlayer 140 a. Beneficially, the mesh second layer 140 b comprises aplurality of strands extending perpendicularly from the interiorsurfaces of first layer 140 a.

A dielectric layer 150 and an upper electrode 160 are sequentiallydisposed on lower electrode 140, thereby completing capacitor C.

FIGS. 3A to 3J are cross sectional views explaining a method of formingthe capacitor shown in FIG. 2.

FIG. 3A illustrates a step of forming contact plug 115 on semiconductorsubstrate 100.

Referring to FIG. 3A, a device isolation layer (not shown) is formed onsemiconductor substrate 100 by a conventional device isolation process,thus defining an active region on substrate 100. Then, a devicestructure (not shown) having a capacitor contact region is formed on theactive region. The device structure includes a transistor and a bitline, and the capacitor contact region includes a source region, or alanding pad region disposed on the source region.

An oxide material with a good planarization characteristic such as aborophospho silicate glass (BPSG), a spin on glass (SOG), or an undopedsilicate glass (USG) is deposited on substrate 100 to form insulatinglayer 105. Insulating layer 105 is partially etched away by aphotolithography process, thus contact hole 110 is formed to expose thecapacitor contact region.

A conductive layer such as a doped polysilicon layer is formed oninsulating layer 105 to a thickness sufficient to fill contact hole 110.Then, the conductive layer is removed by an etch-back process or a CMPprocess to expose a top surface of insulating layer 105. Accordingly,contact plug 115 formed in contact hole 110 is electrically contactedwith the capacitor contact region.

FIG. 3B illustrates a step of forming a storage node hole to exposecontact plug 115.

Referring to FIG. 3B, an oxide such as a tetra ethyl ortho silicate(TEOS) is deposited on contact plug 115 and insulating layer 105 by, forexample, a high-density plasma-chemical vapor deposition process, toform mold layer 120.

A photoresist film is formed on mold layer 120, and then the photoresistfilm is exposed and developed. Accordingly, photoresist pattern 125 isformed on mold layer 120.

Mold layer 120 is partially etched away using photoresist pattern 125 asan etching mask to form a storage node hole 130 near contact plug 115and a portion of insulating layer 105 around contact plug 115.

FIGS. 3C to 3E illustrate steps of providing a catalyst 136 onto abottom and sidewalls of storage node hole 130.

A catalyst preferably includes a material to be ionized in mold layer120 such as titanium (Ti), chromium (Cr), iron (Fe), manganese (Mn), oralkali earth metals. For example, the catalyst may be provided by asolution injection method using an electronegativity difference, adoping method using plasma energy, a diffusion injection method usingthermal energy, or an ion injection method. As an exemplary embodiment,the catalyst is injected by the solution injection method using anelectronegativity difference.

As shown in FIG. 3C, alkali earth metals are used as catalyst 136. Anaqueous solution 135 of alkali earth metals (•) is supplied onto asurface of substrate 100. Aqueous solution 135 additionally containsnegative ions (□) such as OH⁻ ions and positive ions (Δ) such as H⁺ions.

Referring to FIG. 3D and FIG. 3E, a catalyst layer 138 is formed on thebottom and the sidewalls of storage node hole 130 and on the top surfaceof photoresist pattern 125. Water in catalyst layer 138 is removed usinga spin dryer. As a result, catalyst 136 permeates through the bottom andthe sidewalls of storage node hole 130 and on the top surface ofphotoresist pattern 125.

FIG. 3F illustrates a step of forming first and second layers 140 a and140 b of lower electrode 140.

Referring to FIG. 3F, after the permeation of catalyst 136, photoresistpattern 125 is removed by ashing and stripping processes.

As an exemplary embodiment, first layer 140 a of doped polysilicon layeris formed on the bottom and sidewalls of storage node hole 130 and onthe top surface of mold layer 120. For example, an N-doped polysiliconmaterial is deposited to a thickness of about 400 Å to 450 Å by alow-pressure chemical vapor deposition (LPCVD) process under atemperature of about 500° C. to 520° C., and a pressure of about 180 Pato 190 Pa. Source gases for the LPCVD process such as a silane (SiH4)gas is provided at a flow rate of about 0.5 standard liter per minute(slm) and a phosphine (PH3) gas is provided at a flow rate of about 200standard cubic centimeter per minute (sccm). While first layer 140 a isformed, a 3-dimensional polysilicon mesh grows by the activation ofcatalyst 136 to form mesh second layer 140 b. As an exemplaryembodiment, mesh second layer 140 b grows perpendicularly from surfacesof the first layer 140 a.

The diameter of strands of the mesh second layer 140 b is proportionalto the deposition time of first layer 140 a. Therefore, minimizing thefirst layer 104 a deposition time will decrease the diameter of secondlayer 104 b by several tens of Å, and maximize the surface area of lowerelectrode 140. In addition, if the diameter of second layer 140 bincreases, the second layer 140 b warps due to an increase in the innerstress. Minimizing the deposition time of first layer 140 a ensures thatsecond layer 140 b grows in a relatively straight line, thereby secondlayer 140 b grows perpendicularly from the first layer 140 a.

FIG. 3G illustrates a step of forming a sacrificial layer 145 on lowerelectrode 140.

Referring to FIG. 3G, an oxide material such as SOF or USG is depositedon first and second layers 140 a and 140 b to a thickness sufficient tofill storage node hole 130 and form sacrificial layer 145.

FIG. 3H illustrates a step of forming lower electrode 140.

Referring to FIG. 3H, first layer 140 a is removed by an etch-back or aCMP process until the top surface of mold layer 120 is exposed.

Although FIGS. 3C–3F show an embodiment where the photoresist pattern125 is removed after the injection of catalyst 136 and after secondlayer 140 b is grown, alternatively catalyst 136 may be injected to thebottom and sidewalls of storage node hole 130 after removing photoresistpattern 125. For example, after photoresist pattern 125 is completelyremoved, a catalyst is injected on the top surface of mold layer 120,the bottom and sidewalls of storage node hole 130. Therefore, secondlayer 140 b also grows on first layer 140 a disposed on the top surfaceof mold layer 120. As a result, when first layer 140 a is removed fromlayer 120 by an etch-back process or a CMP process, an additional stepand time are saved.

FIG. 3I illustrates a step of completing lower electrode 140 ofcapacitor C, and FIG. 3J is a plan view illustrating lower electrode 140of capacitor C.

Referring to FIGS. 3I and 3J, sacrificial layer 145 and mold layer 120are completely removed by a wet etching process, thus completing theformation of lower electrode 140 of capacitor C. As an exemplaryembodiment, a limulus amebocyte lysate (LAL) solution is used as anetching solution in the wet etching step. The LAL solution is a mixtureof ammonium fluoride, hydrofluoric acid, and de-ionized water.

As shown in FIG. 3J, mesh second layer 140 b is disposed insidecylindrical first layer 140 a, having first members extendingperpendicularly (upward) from the bottom of first layer 140 a, and thenhaving second members extending perpendicularly in both directions fromthe first members across the interior cross-section of the cylindricalfirst layer 140 a.

Again referring back to FIG. 2, dielectric layer 150 having a highdielectric constant such as an oxide/nitride/oxide layer (ONO layer) isformed on lower electrode 140. Subsequently, an upper electrode 160,such as a doped polysilicon layer, is formed on dielectric layer 150 tocomplete the capacitor having an increased surface area.

Since the 3-dimensional mesh structure substantially increases thesurface area of the lower electrode, the height of the capacitor can bereduced for the same capacitance compared to a similar capacitorstructure without the mesh. Accordingly, the step difference between thecapacitor region and the non-capacitor region of the substrate isminimized. Furthermore, a single mold layer is formed to pattern thelower electrode, thus simplifying the process of forming the capacitorand improve process efficiency.

Although the exemplary embodiments of the present invention have beendescribed, it is understood that the present invention should not belimited to these exemplary embodiments but various changes andmodifications can be made by one skilled in the art within the scope ofthe present invention as hereinafter claimed.

1. A method of forming a capacitor for a semiconductor device,comprising: forming a mold layer on a semiconductor substrate; etchingthe mold layer to form a storage node hole that exposes a conductiveregion of the semiconductor substrate; providing a catalyst into thestorage node hole; forming a lower electrode having a first layer and amesh second layer connected to the first layer, the first layer beingconnected to a conductive region of the semiconductor substrate; forminga dielectric layer on the lower electrode; and forming an upperelectrode on the dielectric layer.
 2. The method of claim 1, furthercomprising, prior to forming the mold layer: forming an insulating layeron the semiconductor substrate; forming a contact hole for exposing theconductive region of the semiconductor substrate by etching theinsulating layer; and forming a contact plug in the contact hole.
 3. Themethod of claim 1, wherein forming the storage node hole includes:forming a photoresist pattern on the mold layer; and etching the moldlayer using the photoresist pattern as an etching mask.
 4. The method ofclaim 3, further comprising removing the photoresist pattern afterproviding the catalyst.
 5. The method of claim 1, wherein the catalystincludes a material to be ionized.
 6. The method of claim 5, wherein thematerial to be ionized is one selected from the group consisting oftitanium (Ti), chromium (Cr), iron (Fe), manganese (Mn), and alkaliearth metals.
 7. The method of claim 6, wherein the catalyst furtherincludes negative ions and positive ions.
 8. The method of claim 1,wherein the catalyst is provided by one of a solution injection methodusing an electronegativity difference, a doping method using plasmaenergy, a diffusion injection method using thermal energy, or an ioninjection method.
 9. The method of claim 1, wherein forming the lowerelectrode includes: forming the first layer in the storage node hole andon a top surface of the mold layer; growing the mesh second layer fromthe first layer using the catalyst; forming a sacrificial layer on thefirst and second layers that fills the storage node hole; removing aportion of the first layer, thereby exposing the top surface of the moldlayer; and removing the mold layer and the sacrificial layer.
 10. Themethod of claim 1, wherein water is removed from the catalyst prior togrowing the second mess layer.
 11. The method of claim 1, wherein thefirst layer is formed in a cylindrical shape, and the mesh second layeris formed inside the cylindrical first layer.